Photolithography or optical lithography is generally known as a process that is used in micro fabrication to selectively remove parts of thin films on a substrate. Photolithography generally uses a directed light source to transfer a geometric pattern from a photomask to a light-sensitive chemical resist material that is formed on the substrate, thus generating an exposure pattern in the resist material from the light radiation. A series of chemical treatments may then be used to etch or otherwise transfer the exposure pattern into one or more thin film layers positioned underneath the resist layer.
More recent lithography-type systems for micro fabrication operate to transfer or generate an exposure pattern in a resist layer without the intermediary step of creating a photomask. For example, a direct-write (DW) exposure tool operates to write patterns directly into one or more layers on a substrate. The pattern is generally written from an electronic or computer-type file that is used to control a precision exposure source that may be selectively directed onto the layers of the substrate. More particularly, a DW exposure tool is generally configured such that the exposure of a circuit pattern is made not by illumination of the photo-resist through a mask or film negative of the circuit, but rather by directly and selectively exposing the desired areas of the resist or other layer on a substrate with a focused beam of the appropriate energy and dosage to create the desired circuit pattern. However, monitoring and controlling an overlay of the beam is complex, and thus may result in poor performance.